Women with endometriosis often have significant pain. Modern studies have implicated the neo-innervation of endometrial cysts as a primary source of this pain. However, the presence of nerve fibers does not necessarily specify their function and cannot determine whether, or in which situations, they are active. There has been no investigation to functionally characterize the effect of endometrial lesions on nerves or on axons. Our laboratory has focused on the effects of inflammation on axons. We have shown that nerve inflammation induces ectopic mechanical sensitivity of nociceptor axons, which are not normally sensitive. Our data also indicate that nerve inflammation induces ongoing activity that arises from both the inflamed site and / or the cell body, and that sympathetic neuronal activity is decreased during nerve inflammation. Recently we adapted the model of rat endometriosis to involve the sciatic nerve. This model is very similar to the rat endometriosis model where a section of uterus is transplanted to a intraperitoneal site. In preliminary data, a uterine section was transplanted to the sciatic nerve. Three complimentary electrophysiological methods are proposed to determine the characteristics of the effect of uterus, endometrium, and myometrium on the sciatic nerve. First, the proportion of through-conducting axons will be determined. Then, teased fiber recordings will be made from the dorsal roots in some experiments and from the distal end of peripheral nerves in other experiments. This combination of methods offers the advantage that sensory and sympathetic axons that pass through the cyst, as well as those innervating the cyst, can be studied. We will determine if the axons passing in close proximity to the cyst or directly innervating the cyst develop ongoing activity and / or mechanical sensitivity. Recordings will be made 3 months post surgically, after the cysts become stable, and the results compared to myometrium or fat transplant, and unoperated nerves. Because preliminary results revealed the presence of intraneural immune cells, we will determine whether the lesions of endometriosis damage axons. Importantly, we will use not only full thickness uterus, but also isolated endometrium and myometrium, and evaluate the viability of these specific tissues to form cysts. Using immunohistological methods, we will determine the extent of neutrophil and macrophage invasion of the nerve-uterus complex. We will also determine if axons are damaged using ninjurin and fluoro-jade, assessing the presence in both axons and dorsal root ganglion cells. These studies will determine the function and thus the importance of the ectopic innervation of endometrial cysts, as well as the effects of the lesions on through-conducting axons. The results of this study will impacts the understanding of endometriosis pain and seed further research into the pain mechanisms of endometriosis. PUBLIC HEALTH RELEVANCE: In these studies we plan to develop our recently developed model of sciatic endometriosis to make novel inquiries regarding the etiology of endometriosis-related pain. The information that this study will yield stands to improve diagnostic awareness and mechanistic understanding, and thus therapeutic approaches, of the treatment of the symptoms of endometriosis. As a result of this research, consideration and specific examination of nerves within the pelvis during ablative laparoscopic techniques may become an important additional diagnostic procedure for women with endometriosis.